To accomplish blood compatibility for different materials in contact with blood one of the most important methods has been to heparinize the surface thereof. Thus, the heparin layer on the surface inhibits, as was mentioned above, the adhesion of thrombocytes and the adsorption of blood proteins. Furthermore, the heparin must be enzymatically active in the blood coagulation process, which calls for specific necessities as to molecular conformation and mobility relative to the surface.
Two main principles for the heparinization have previously been utilized. The first one is based on colloidal precipitation, e.g. through complex-formation between amphiphilic amines and heparin. The second one utilizes the possibility of covalently bonding the heparin to the surface. However, these known principles have some limitations which means that there is continuous research for alternative or improved methods for the heparinization.